1. Field of the Invention
The present invention relates to the field of liquid crystal display, and in particular to retention of optic films in a backlight module.
2. The Related Arts
Liquid crystal display (LCD) has a variety of advantages, such as thin device body, low power consumption, and being free of radiation, and is thus widely used. Most of the LCDs that are currently available in the market are backlighting LCDs, which comprise a liquid crystal panel and a backlight module. The operation principle of the liquid crystal panel is that liquid crystal molecules are interposed between two parallel glass substrates and the liquid crystal molecules are controlled to change direction by application of electricity in order to refract light emitting from the backlight module for generating images. Since the liquid crystal panel itself does not emit light, light must be provided by the backlight module in order to normally display images. Thus, the backlight module is one of the key components of an LCD. The backlight module can be classified in two types, namely side-edge backlight module and direct backlight module, according to the position where light gets incident. The direct backlight module arranges a light source, such as a cold cathode fluorescent lamp (CCFL) or a light-emitting diode (LED) at the back side of the liquid crystal panel to form a planar light source that directly provides lighting to the liquid crystal panel. The side-edge backlight module arranges a backlight source of LED light bar at an edge of a backplane to be located rearward of one side of the liquid crystal panel. The LED light bar emits light that enters a light guide plate (LGP) through a light incident face formed at one side of the light guide plate and is projected out through a light emergence face of the light guide plate, after being reflected and diffused, to thereby form a planar light source for the liquid crystal panel.
A backlight source often includes optic films for light diffusion and condensation in order to provide an appropriate light shape. These optic films are generally made of PET (Polyethylene Terephathalate) and have a small thickness, usually between 0.1-0.6 mm, making it very easy to warp. For small-sized backlight modules, the optic films are often formed with lugs on opposite sides for mounting. For large-sized backlight modules, as shown in FIG. 1, an optic film 100 is generally mounted in a suspended fashion. For such a suspension fashion, suspending pegs 200 are usually of a cylindrical form and are uniformly distributed. The suspending pegs 200, which are cylindrical in shape, form point contact with the optic film 100. The portion of the optic film 100 between two suspending pegs 200 shows a gravitational force, which induces a torque with the suspending peg 200 as a fulcrum, causing the optic film 100 to move toward the middle. As shown in FIGS. 2A and 2B, the moving distance is the gap that is preserved between the optic film 100 and the suspending pegs 200. Once the optic film 100 has moved toward the middle, since a gap is present between the optic film 100 and the liquid crystal panel, it is no longer possible to constrain warp of the optic film 100 as shown in FIG. 3 and the image displayed shows inconsistent brightness. To eliminate such a problem, suspending pegs 300 are made in a planar form or the distance between two suspending pegs is shortened. These improve the warp of the optic film 100 to some extents. However, due to general insufficiency of space is available in structure design, it is not possible to unlimitedly shorten the distance between two pegs and the torque caused by gravitational force still exists, as shown in FIG. 4. Further, the optic films are made of PET plastics, they inevitably shows thermal expansion. This makes it impossible to completely eliminate warp of the optic films.